Health and Environmental agencies require waste water to be collected and directed to a proper receptacle, such as a municipal sewer or private septic tank. The term "waste water" includes used or dirty process water (known as gray water), and sewage water (commonly referred to as black water). Gray water may be generated from a variety of different operations. In a grocery store, for example, water is used in deli, food service, and floral departments for cleaning, maintenance, and other purposes. Refrigerated display cases generate additional process water from condensate and defrost procedures. The waste water generated from these various sources must be collected and transported to the proper receptacle.
In the past, conventional gravity drainage piping has been used to collect and transport waste water. Gravity drainage systems use collection points located below the waste water source which feed into drainage pipes leading to a sewer line. The piping in such systems must be continuously sloped so that the waste water flows all the way to the sewer line. As a result, pipes for gravity drainage systems are often laid in or underneath the concrete pad supporting the facility. This process not only requires significant amounts of additional plumbing work, but also complicates changes in facility layout, which require portions of the concrete pad to be ripped up to expose drainage channels.
More recently, vacuum drainage systems have been used to collect and transport waste water. A vacuum drainage system typically comprises a collection drain located under each waste water source, each collection drain leading to a common drain pipe. The drain pipe is connected to a pump which creates negative pressure in the drain pipe to thereby pull liquid through the drain pipe and into the collection tank. The tank has a drain that is typically positioned over a sewer line to allow the tank to be emptied.
Significantly, vacuum drainage systems allow the use of overhead drainage piping since suction rather than gravity is used to transport the waste water. Vacuum drainage piping does not need to be laid in concrete below the waste water source, but instead may follow overhead electrical and refrigeration service lines. Thus, plumbing layouts are simplified and water generating equipment may be quickly and easily relocated within a facility without ripping up concrete. As a result, greater freedom exists for redesigning the facility layout.
While the use of overhead piping provides certain advantages, the pumps used in vacuum drainage systems are capable of lifting only a limited volume of water from the collection drains to the vacuum drainage piping. Certain systems provide a buffer section consisting of a large diameter pipe into which waste water initially collects. An air intake is provided to allow air at atmospheric pressure to access liquid in the pipe. Once the desired volume of water has collected in the buffer, a valve leading to the vacuum drainage piping is opened so that waste water travels toward the valve. Air entering the intake opening creates a pressure differential across the waste water which acts to lift the waste water toward the vacuum drainage piping. Once the waste water reaches the vacuum drainage piping, the valve shuts so that additional water may collect in the buffer and the process is repeated. In this manner, conventional vacuum drainage systems lift discrete volumes or "slugs" of waste water to the vacuum drainage piping.
It is difficult, however, for such conventional systems to ensure that an appropriate volume of waste water is pulled toward the vacuum drainage piping. Care must be taken so that the slug of waste water is not too large for the pump. Conversely, slugs that are too small cause unduly rapid cycling of the valve. As a result, it is overly difficult to efficiently transport unbroken slugs of liquid using conventional vacuum drainage systems.